1. Field of the Invention
The present invention relates in general to a flow coater for coating a surface of a plate member such as a printed board with coating liquid such as photo resist liquid by causing the coating liquid to flow down onto the surface of the plate member curtainly, i.e., in the form of a curtain, and more particularly to a temperature controller for controlling the temperature of a coating liquid on which the change in property such as viscosity of the coating liquid depends on the plate member in order to control a thickness of a coating layer.
2. Description of the Related Art
A flow coater of this kind is constructed to employ the so-called curtain flow method wherein the coating is carried out in such a way that the coating liquid is caused to flow down curtainly through a gap of a nozzle of a supply head while a plate member is conveyed. In general, the flow coater is employed for the coating processing, such as surface coating, required for a plate member for use in a building material. In this case, the coating thickness depends on the property, such as viscosty, of the coating liquid, and in particular it is changed due to the variation of temperature of the coating liquid.
The temperature of the coating liquid is changed during coating as well as during vacation in the seasons and the variation of the ambient temperature in mornings and evenings. In particular, a pump for circulating the coating liquid is heated during the operation thereof and heat thus generated is transmitted to the associated portions. This results in a rise in the temperature of the coating liquid.
In order to suppress the temperature rise in the coating liquid, a large scale stirrer is installed in a supply tank so that the necessary work progresses while the coating liquid is continuously stirred. However, it is said that this is not sufficient for the coating processing. Therefore, management of the temperature of the coating liquid needs to be more positively carried out. For this reason, there is installed a temperature controller for either cooling or heating the coating liquid in correspondence with the change in the temperature of the coating liquid. In the temperature controller, the heat exchange is carried out between a temperature controlling medium such as water which is circulated from a supply source thereof and the coating liquid via a heat exchanger unit, thereby adjusting the temperature of the coating liquid. In this connection, conventionally, in general, there has been adopted a temperature controlling method wherein the heat exchanger unit is applied to the supply tank so that the coating liquid is cooled or heated properly by the temperature controller while monitoring the temperature of the coating liquid in the tank.
However, in the conventional method wherein the heat exchanger unit is applied to the supply tank in order to carry out the temperature control, there arises a problem in that it is impossible to carry out a temperature control corresponding speedily and accurately to the variation of the liquid temperature. This results because the capacity of the coating liquid in the tank is large, the responsibility of the heat exchanger unit is poor, and hence even when the coating liquid in the tank is stirred by a stirrer, the sufficient improvement can not be obtained. For this reason, the temperature control by the temperature controller can not sufficiently cope with the variation of temperature of the coating liquid which is supplied from the supply head onto the plate member. As a result, the property, such as the viscosity of the coating liquid, can not be stabilized, and hence it is impossible to obtain a uniform coating thickness.
In particular, in the case where the plate member to be subjected to coating processing is a printed board, and the photo resist liquid is applied as the coating liquid thereonto, since high accuracy is required for the thickness of the photo resist layer, in the case of utilization of the conventional temperature control, the product yield is poor and hence it is difficult to manufacture a printed board of high quality.